The magenta line shows the 1979 to 2000
median extent for that month. The black cross indicates the geographic North
Pole. Sea Ice Index data. —Credit: National Snow and Ice
Data Center High-resolution image
Arctic sea ice extent increased rapidly
through October, as is typical this time of year. Large areas of open water
were still present in the Beaufort and Chukchi seas at the end of the month.
The open water contributed to unusually warm conditions along the coast of
Siberia and in the Beaufort and Chukchi seas.
Overview of conditions
Average ice extent for October 2011 was 7.10 million square kilometers (2.74
million square miles), 2.19 million square kilometers (846,000 square miles)
below the 1979 to 2000 average. This was 330,000 square kilometers (127,000
square miles) above the average for October 2007, the lowest extent in the
satellite record for that month.
By the end of October, ice extent remained
below the 1979 to 2000 average in the Beaufort and Chukchi seas and in the
Barents and Kara seas. Extent was near average in the East Greenland Sea. New
ice growth has closed both the Northwest Passage and the Northern Sea Route.
Conditions in context
Arctic sea ice extent increased rapidly
through October. Ice extent during October 2011 increased at an average rate of
114,900 square kilometers (44,360 square miles) per day, about 40% faster than
the average growth rate for October 1979 to 2000. On October 30, Arctic sea ice
extent was 8.41 million square kilometers (3.25 million square miles), 226,000
square kilometers (87,300 square miles) more than the ice extent on October 30,
2007, the lowest extent on that date in the satellite record.
During the month of October, the freeze-up
that begins in September kicks into high gear. The rate of freeze-up depends on
several factors including the atmospheric conditions and the amount of heat in
the ocean that was accumulated during the summer. However, each decade, the
October extent has started from a lower and lower point, with the record low
extent during the 1980s (1984) substantially higher than the record low extent
during the 1990s (1999), which in turn is substantially higher than the record
low extent during the 2000s (2007).
October 2011 compared
to past years
Ice extent for October 2011 was the second
lowest in the satellite record for the month, behind 2007. The linear rate of
decline for October over the satellite record is now -61,700 square kilometers
(-23,800 square miles) per year, or -6.6% per decade relative to the 1979 to
In recent years, low sea ice extent in the
summer has been linked to unusually warm temperatures at the surface of the
Arctic Ocean in the fall. This pattern appeared yet again this fall.
Air temperatures over most of the Arctic
Ocean for October 2011 ranged from 1 to 4 degrees Celsius (1.8 to 7.2 degrees
Fahrenheit) above average, measured at the 925 millibar level, about 1,000
meters or 3,000 feet above the surface. However, over the eastern Canadian
Arctic and Greenland, temperatures were as much as 3 degrees Celsius (5.4
degrees Fahrenheit) below average.
These temperature anomalies in part reflect a
pattern of above-average sea level pressure centered over the northern Beaufort
Sea, and lower than average sea level pressure extending across northern
Eurasia. This pattern is linked to persistence of the positive phase of the
Arctic Oscillation through most of the month.
These pressure and temperature
anomalies tend to bring in heat from the south, warming the Eurasian coast, but
they also lead to cold northerly winds over the eastern Canadian Arctic
However, along the Siberian coast and in the Beaufort and Chukchi
seas, warmer temperatures came primarily from the remaining areas of open water
in the region, as heat escaped from the water. These effects are more strongly
apparent in the surface air temperatures: average October temperatures in the
region were 5 to 8 degrees Celsius (9.0 to 14.4 degrees Fahrenheit) above average.
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